1. Field of the invention
This invention relates to a geophysical electrode and more particularly to a non-polarized geophysical electrode applicable for conducting measurements of geoelectric field signals in the ground to determine underground composition in geophysical prospecting.
2. Background Art
Geophysical electrodes have been used for measuring telluric current signals, earthquake signals, and electrical potential from the earth ground especially in various geophysical measurement methods such as MT (magnetotelluric), AMT (audio-magnetotelluric), IP (induced polarization), and resistivity measurement. In geophysical prospecting, a plurality of electrodes are employed for measuring and mapping the ground potential signals in a geoelectric field at a selected ground site. A plurality of electrodes are inserted into the ground at a plurality of selected locations of the site. The correlation of the ground potential in geoelectric field signal measurements obtained at those locations enables a determination of the mineral deposit at the site. Presently, non-polarized electrodes are employed for carrying out the measurements. Such electrode generally consists of a tubular enclosure having a porous bottom cover plate or alternatively having a porous tubular container mounted at its lower end. Commonly, porous ceramic or gypsum is used for making the cover plate or the lower tubular container. The electrode is filled with an electrolyte consisting of a chemical reaction compound such as copper sulfate (CuSO4) or lead chloride (PbCl2) solution. A copper (Cu) or lead (Pb) rod located inside the electrode extends from a lead wire terminal provided at the upper cover of the enclosure to the bottom of the chemical electrolyte within the electrode.
In application, it is necessary to dampen the ground of a prospecting site with an electrolytic compound solution such as a solution of sodium chloride, then a plurality of the measuring electrodes are inserted into the wetted ground at various selected locations of the site to measure the geoelectric field signals at those locations. With the insertion of the porous lower portion of the electrode into the ground, the chemical reaction compound of electrolyte in the electrode would inherently leach from the electrodes into the ground through the porous lower portion thus causing undesirable environmental pollution. The leaching of the electrolytic compound into the ground would also deplete the amount of the electrolytic compound within the electrode with each use of the electrode and therefore invariably reducing useful life of the electrode. Additionally, the amount of electrolyte can moreover be depleted by evaporation through the porous portion of the electrode housing. Furthermore, the effectiveness of the electrode is greatly reduced in cold weather condition when air temperature is lower than −10° C. causing freezing of its fluidic electrolyte.
In order to prevent the evaporation of the electrolyte from the porous lower plate or lower tubular portion of the electrode housing, it is a necessary to cover the electrode with a wet covering pad or wrapping material during storage, which is messy to carry out.
Moreover, the effective contact surface between the electrode and the ground is also restricted by the small size and diameter of the tubular porous portion of the electrode housing.
Still furthermore, such electrode filled with reaction chemical electrolytic solution is difficult to handle and transport without causing leakage of the chemical compound in such circumstances, and it is also hazardous to the health of the workers fabricating the electrode due to the inherent exposure of the workers to the toxic copper sulfate or the lead in the lead chloride of the chemical reaction compound in the electrolyte.